Dual-Mode Oscillator and Multi-Phase Oscillator

ABSTRACT

A dual-mode oscillator and a multi-phase oscillator includes a mode switching circuit to switch between two operating modes and obtain oscillation signals having two different bands. The dual-mode oscillator also includes two transformer-coupled oscillators and a step-up transformer in the transformer-coupled oscillators where the step-up transformer multiplies a drain voltage swing of a first MOS transistor and then injects a voltage signal to a gate of a second MOS transistor to obtain a larger gate voltage swing without increasing a supply voltage of the oscillator. The dual-mode oscillators are connected through multi-phase coupled circuits to form a Mobius loop.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority to Chinese PatentApplication No. 201610966245.9, filed on Nov. 4, 2016, which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

This application relates to the field of oscillator technologies, and inparticular, to a dual-mode oscillator and a multi-phase oscillator thatis based on the dual-mode oscillator.

BACKGROUND

An oscillator is an energy conversion apparatus that converts directcurrent electric energy into alternating current electric energy havinga specific frequency. It is widely applied to multiple fields such asmeasurement, automatic control, wireless communications, and remotecontrol. In a wireless communications system, an oscillator (forexample, a carrier oscillator of a transmitter) is mainly used togenerate and output multi-frequency oscillation signals. Operatingbandwidth of the wireless communications system depends on a frequencyrange of the oscillation signals. With development of the wirelesscommunications system, the wireless communications system needs to havelarger operating bandwidth, and the oscillator used in the system needsto output oscillation signals having a frequency range as wide aspossible. A dual-mode oscillator can break a frequency range limitationof a conventional oscillator (for example, an LC oscillator) and provideoscillation signals having a wider frequency range, and therefore ismore applied to existing wireless communications systems.

As shown in FIG. 1, an existing dual-mode oscillator usually includestwo LC (inductor-capacitor) oscillators and one mode switching circuit.Each LC oscillator includes a pair of transistors and an LC oscillationcircuit. Two switch groups, that is, switches S1 and S2 and switches S3and S4, in the mode switching circuit are alternately turned on, so thatthe two LC oscillators are in two different operating modes. When S1 andS2 are turned on and S3 and S4 are turned off, the two LC oscillatorsare in an in-phase mode, and an oscillation signal frequency range ofthe dual-mode oscillator is the same as a frequency range of a single LCoscillator. When S1 and S2 are turned off and S3 and S4 are turned on,the two LC oscillators are in a reverse-phase mode, and an oscillationsignal frequency range is lower than that in the in-phase state. Becausethe dual-mode oscillator has a high frequency range and a low frequencyrange respectively in the two operating modes, compared with theconventional oscillator, the dual-mode oscillator can provide anoscillation signal having a wider frequency range.

Though the existing dual-mode oscillator can provide and outputoscillation signals having a wide band, phase noise performance of theexisting dual-mode oscillator is relatively poor, which is one ofimportant factors limiting performance of a communications system.Therefore, it is necessary to provide a new oscillator, to ensure goodphase noise performance while providing wide-band oscillation signalsfor output.

SUMMARY

This application provides a dual-mode oscillator and a multi-phaseoscillator, to ensure good phase noise performance while providingwide-band oscillation signals for output.

According to a first aspect, an embodiment of this application providesa dual-mode oscillator, including two transformer-coupled oscillatorsand a mode switching circuit, where each transformer-coupled oscillatorincludes a differential metal oxide semiconductor (MOS) transistor pair,a primary capacitor Cp, a secondary capacitor Cs, and a step-uptransformer; a source of a first MOS transistor in the differential MOStransistor pair and a source of a second MOS transistor in thedifferential MOS transistor pair are connected, and coupled to aconstant-voltage node; a drain of the first MOS transistor is separatelyconnected to one end of the primary capacitor Cp and a first input endof the step-up transformer, and a drain of the second MOS transistor isseparately connected to the other end of the primary capacitor Cp and asecond input end of the step-up transformer; a gate of the first MOStransistor is separately connected to one end of the secondary capacitorCs and a second output end of the step-up transformer, and a gate of thesecond MOS transistor is separately connected to the other end of thesecondary capacitor Cs and a first output end of the step-uptransformer, where the first input end and the first output end aredotted terminals; and the mode switching circuit is located between thetwo transformer-coupled oscillators, separately connected to two drainsof each transformer-coupled oscillator, and configured to change anoscillation frequency range of output of the dual-mode oscillator bymeans of switching.

Optionally, an output end of the dual-mode oscillator is the two drainsor the two gates of any transformer-coupled oscillator.

In the dual-mode oscillator provided in this embodiment of thisapplication, switching between two operating modes is implemented byusing the mode switching circuit, so that oscillation signals having twodifferent bands can be obtained, and values of a primary capacitor Cpand a secondary capacitor Cs in each transformer-coupled oscillator andcapacitors C_(mode) in the mode switching circuit may be tuned to outputoscillation signals having a wide band. In addition, the dual-modeoscillator in this embodiment of this application includes twotransformer-coupled oscillators, and a drain of a first MOS transistorin each transformer-coupled oscillator is connected to a gate of asecond MOS transistor through a step-up transformer, that is, thestep-up transformer multiplies a drain voltage swing of the first MOStransistor and then injects a voltage signal to the gate of the secondMOS transistor, so that a larger gate voltage swing is obtained withoutincreasing a supply voltage of the oscillator, and phase noiseperformance of the dual-mode oscillator is improved. Moreover, in thedual-mode oscillator, the two transformer-coupled oscillators arecoupled through the mode switching circuit, so that the phase noiseperformance can be further improved.

In a possible implementation, the first MOS transistor and the secondMOS transistor are both N-channel MOS (NMOS) transistors; the source ofthe first NMOS transistor and the source of the second NMOS transistorare connected, and coupled to the constant-voltage node; and theconstant-voltage node is directly grounded, or the constant-voltage nodeis grounded through a tail current source.

In a possible implementation, a center tap of a primary inductor Lp ofthe step-up transformer is connected to a power supply voltage V_(DD),and a center tap of a secondary inductor Ls of the step-up transformeris connected to a bias voltage V_(gate).

In a possible implementation, the first MOS transistor and the secondMOS transistor are both P-channel MOS (PMOS) transistors; the source ofthe first PMOS transistor and the source of the second PMOS transistorare connected, and coupled to the constant-voltage node; and theconstant-voltage node is directly connected to a power supply voltageV_(DD), or the constant-voltage node is connected to a power supplyvoltage V_(DD) through a tail current source.

In a possible implementation, a center tap of a primary inductor Lp ofthe step-up transformer is grounded, and a center tap of a secondaryinductor Ls of the step-up transformer is connected to a bias voltageV_(gate).

In a possible implementation, at least one of the primary capacitor Cpor the secondary capacitor Cs includes at least one of a switchcapacitor array or a variable capacitance diode, which is tunable by atuning signal.

In this implementation, if the primary capacitor Cp and the secondarycapacitor Cs each include a switch capacitor array and a variablecapacitance diode, stepped tuning on capacitance of the primarycapacitor Cp and the secondary capacitor Cs can be implemented bychanging quantities of enabled capacitors in switch capacitor arrays, tofurther implement stepped tuning on an oscillation frequency of thetransformer-coupled oscillator; and continuous fine tuning on thecapacitance of the primary capacitor Cp and the secondary capacitor Cscan be implemented by tuning control voltages of variable capacitancediodes, to further implement continuous fine tuning on the oscillationfrequency of the transformer-coupled oscillator.

In a possible implementation, the mode switching circuit includes acontrol circuit and at least two mode capacitors C_(mode) coupled to thecontrol circuit; and the control circuit is configured to switch thedual-mode oscillator between an odd mode and an even mode under aneffect of a mode control signal, where in the odd mode, the modecapacitors C_(mode) are equivalent to being bypassed, and theoscillation frequency range is a first oscillation frequency range; andin the even mode, the mode capacitors C_(mode) are equivalent tobridging the two drains of each transformer-coupled oscillator, and theoscillation frequency range is a second oscillation frequency range,where the second oscillation frequency range is different from the firstoscillation frequency range.

In a possible implementation, the second oscillation frequency range islower than the first oscillation frequency range.

In a possible implementation, the control circuit includes a first oddmode switch and a second odd mode switch, and a first even mode switchand a second even mode switch; the first even mode switch and the secondeven mode switch are each connected in parallel to at least one of themode capacitors; two ends of the first even mode switch are respectivelyconnected to drains of first MOS transistors of the twotransformer-coupled oscillators, and two ends of the second even modeswitch are respectively connected to drains of second MOS transistors ofthe two transformer-coupled oscillators; and two ends of the first oddmode switch are respectively connected to a drain of a first MOStransistor of one transformer-coupled oscillator and a drain of a secondMOS transistor of the other transformer-coupled oscillator, and two endsof the second odd mode switch are respectively connected to a drain of asecond MOS transistor of the one transformer-coupled oscillator and adrain of a first MOS transistor of the other transformer-coupledoscillator, where in the odd mode, the first odd mode switch and thesecond odd mode switch are turned on, and the first even mode switch andthe second even mode switch are turned off; and in the even mode, thefirst odd mode switch and the second odd mode switch are turned off, andthe first even mode switch and the second even mode switch are turnedon.

In the foregoing implementation, the two odd mode switches and the twoeven mode switches both can be implemented by using MOS transistorsoperating in an on/off state, and the switches are controlled by using amode control signal to be turned on and turned off, to switch anoperating mode of the dual-mode oscillator between the odd mode and theeven mode. In the even mode, the mode capacitors C_(mode) are bypassedby the even mode switches that are turned on, the oscillation frequencyrange of the dual-mode oscillator is the same as an oscillationfrequency range of a single transformer-coupled oscillator. In thiscase, the oscillation frequency range of the single transformer-coupledoscillator can be tuned by tuning values of the primary capacitor Cp andthe secondary capacitor Cs, to tune an oscillation frequency range of ahigh-frequency oscillation signal of the dual-mode oscillator. In theodd mode, the mode capacitors C_(mode) are equivalent to bridging twodrain ends of the transformer-coupled oscillator, so that draincapacitance of the dual-mode oscillator increases, and the oscillationfrequency range is lower than the oscillation frequency range of thesingle transformer-coupled oscillator. In this case, an oscillationfrequency range of a low-frequency oscillation signal of the dual-modeoscillator can be tuned by tuning a value of C_(mode).

According to a second aspect, this application further provides amulti-phase oscillator, including N dual-mode oscillators in anyimplementation above and N multi-phase coupled circuits, where N is aninteger greater than 1; and each multi-phase coupled circuit is coupledbetween two dual-mode oscillators; and a Mobius loop connection isformed by the N dual-mode oscillators and the N multi-phase coupledcircuits.

Optionally, in the Mobius loop connection, N−1 multi-phase coupledcircuits are directly coupled between two corresponding dual-modeoscillators, and one multi-phase coupled circuit is cross-coupledbetween two corresponding dual-mode oscillators.

In a possible implementation, the N dual-mode oscillators and the Nmulti-phase coupled circuits form N stages, each stage includes onedual-mode oscillator and one multi-phase coupled circuit, a firstcoupling end of a multi-phase coupled circuit at each stage is connectedto drains of any transformer-coupled oscillator in a dual-modeoscillator at the stage, and a second coupling end of the multi-phasecoupled circuit at each stage is connected to drains of anytransformer-coupled oscillator in a dual-mode oscillator at a nextstage.

In a possible implementation, the N dual-mode oscillators and the Nmulti-phase coupled circuits form N stages, each stage includes onedual-mode oscillator and one multi-phase coupled circuit, a firstcoupling end of a multi-phase coupled circuit at each stage is connectedto two gates of any transformer-coupled oscillator in a dual-modeoscillator at the stage, and a second coupling end of the multi-phasecoupled circuit at each stage is connected to two gates of anytransformer-coupled oscillator in a dual-mode oscillator at a nextstage.

In a possible implementation, the multi-phase coupled circuit includes acoupling MOS transistor pair; a source of a first coupling MOStransistor in the coupling MOS transistor pair and a source of a secondcoupling MOS transistor in the coupling MOS transistor pair areconnected, and directly grounded or grounded through a current source; adrain of the first coupling MOS transistor and a drain of the secondcoupling MOS transistor are used as the first coupling end, andconnected to the two drains or the two gates of any transformer-coupledoscillator in the dual-mode oscillator at the stage; and a gate of thefirst coupling MOS transistor and a gate of the second coupling MOStransistor are used as the second coupling end, and connected to the twodrains or the two gates of any transformer-coupled oscillator in thedual-mode oscillator at the next stage.

In a possible implementation, the multi-phase coupled circuit includes acoupling capacitor pair, a coupling inductor pair, or a couplingmicrostrip.

In the multi-phase oscillator provided in the embodiments of thisapplication, multiple dual-mode transformer-coupled oscillators areconnected through multi-phase coupled circuits to form a Mobius loop, sothat oscillation signals in multiple phases can be generated, and phasenoise performance of the entire oscillator can be improved. Moreover, inthe multi-phase oscillator provided in the embodiments of thisapplication, based on a same mode control signal, phases oftransformer-coupled oscillator pairs in the dual-mode oscillators aresynchronously locked to an in-phase or reverse-phase state by using modeswitching circuits, so that only one transformer-coupled oscillator ineach transformer-coupled oscillator pair needs to be connected to amulti-phase coupled circuit, to determine phase output of an entireoscillator array. It can be learned that, the multi-phase oscillatorprovided in the embodiments of this application has a simple circuitstructure, and a corresponding circuit layout is more easilyimplemented.

BRIEF DESCRIPTION OF THE DRAWINGS

To describe the technical solutions in this application more clearly,the following briefly describes the accompanying drawings required fordescribing embodiments. A person of ordinary skill in the art may stillderive other drawings from these accompanying drawings without creativeefforts.

FIG. 1 is a diagram of a circuit structure of an existing dual-modeoscillator;

FIG. 2 is a diagram of a circuit structure of a dual-mode oscillatoraccording to an embodiment of this application;

FIG. 3A and FIG. 3B are diagrams of a circuit of the dual-modeoscillator shown in FIG. 2 in an even mode;

FIG. 4A and FIG. 4B are diagrams of a circuit of the dual-modeoscillator shown in FIG. 2 in an odd mode;

FIG. 5 is a diagram of a circuit structure of a transformer-coupledoscillator in a dual-mode oscillator according to an embodiment of thisapplication;

FIG. 6 is a diagram of a circuit module of a multi-phase oscillatoraccording to an embodiment of this application;

FIG. 7A and FIG. 7B are diagrams of a circuit structure of a couplingMOS transistor pair-based multi-phase oscillator according toembodiments of this application;

FIG. 8A, FIG. 8B, FIG. 8C and FIG. 8D are diagrams of a circuitstructure of a coupling capacitor pair-based multi-phase oscillatoraccording to embodiments of this application;

FIG. 9A, FIG. 9B, FIG. 9C and FIG. 9D are diagrams of a circuitstructure of a multi-phase oscillator in a gate connection manneraccording to embodiments of this application; and

FIG. 10 is a waveform graph of oscillation signals in multiple phasesgenerated by a multi-phase oscillator according to an embodiment of thisapplication.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following clearly describes the technical solutions in theembodiments of the present disclosure with reference to the accompanyingdrawings in the embodiments of the present disclosure. The describedembodiments are merely a part rather than all of the embodiments of thepresent disclosure. All other embodiments obtained by a person ofordinary skill in the art based on the embodiments of the presentdisclosure without creative efforts shall fall within the protectionscope of the present disclosure.

FIG. 2 is a diagram of a circuit structure of a dual-mode oscillatoraccording to an embodiment of this application. The dual-mode oscillatormay be applied to multiple fields including a wireless communicationssystem.

As shown in FIG. 2, the dual-mode oscillator provided in this embodimentof this application is designed based on a transformer-coupledoscillator, and may specifically include two transformer-coupledoscillators 210 and 220 and a mode switching circuit 230. Thetransformer-coupled oscillator 210 and the transformer-coupledoscillator 220 are connected through the mode switching circuit 230.

A circuit structure of the transformer-coupled oscillator is firstdescribed. In this embodiment of this application, thetransformer-coupled oscillator 210 and the transformer-coupledoscillator 220 have a same circuit structure, and each include adifferential MOS transistor pair, a primary capacitor Cp, a secondarycapacitor Cs, and a step-up transformer. The following describes aspecific circuit structure of the transformer-coupled oscillator byusing the transformer-coupled oscillator 210 as an example.

As shown in FIG. 2, the transformer-coupled oscillator 210 includes adifferential MOS transistor pair, a primary capacitor Cp, a secondarycapacitor Cs, and a step-up transformer 213.

The differential MOS transistor pair includes a first MOS transistor 211and a second MOS transistor 212. A source of the first MOS transistor211 and a source of the second MOS transistor 212 are connected. A drainof the first MOS transistor 211 is separately connected to one end ofthe primary capacitor Cp and a first input end of the step-uptransformer 213, and a drain of the second MOS transistor 212 isseparately connected to the other end of the primary capacitor Cp and asecond input end of the step-up transformer 213. A gate of the first MOStransistor 211 is separately connected to one end of the secondarycapacitor Cs and a second output end of the step-up transformer 213, anda gate of the second MOS transistor 212 is separately connected to theother end of the secondary capacitor Cs and a first output end of thestep-up transformer 213. If the first MOS transistor 211 and the secondMOS transistor 212 are NMOS transistors, the source of the first MOStransistor 211 and the source of the second MOS transistor 212 aregrounded through a current source or are directly grounded, as shown inFIG. 2. If the first MOS transistor 211 and the second MOS transistor212 are PMOS transistors, the source of the first MOS transistor 211 andthe source of the second MOS transistor 212 are connected to aconstant-voltage directly or through a current source. The followingprovides a specific description with reference to FIG. 5.

For FIG. 2, specifically, the step-up transformer 213 includes a primaryinductor Lp and a secondary inductor Ls, which are respectivelyconnected to a power supply voltage V_(DD) and a bias voltage V_(gate).A dotted terminal of the primary inductor Lp is the first input end ofthe step-up transformer 213, a non-dotted terminal of the primaryinductor Lp is the second input end of the step-up transformer 213.Correspondingly, a dotted terminal of the secondary inductor Ls is thefirst output end of the step-up transformer 213, and a non-dottedterminal of the secondary inductor Ls is the second output end of thestep-up transformer 213. That is, the first input end and the firstoutput end of the step-up transformer 213 are dotted terminals, and thedrains and the gates of the differential MOS transistor pair have areverse-phase relationship with the input end and the output end of thestep-up transformer 213. Step-up times of the step-up transformer 213are k (k>1), that is, a voltage at an output end (equivalent to avoltage at two ends of the secondary capacitor Cs) is k times of avoltage at an input end (equivalent to a voltage at two ends of theprimary capacitor Cp). A step-up function is implemented by means ofcoupling from the primary inductor Lp to the secondary inductor Ls.

The two drains of the differential MOS transistor pair in thetransformer-coupled oscillator are used as an output end of thetransformer-coupled oscillator, and a signal that is output by theoutput end is an oscillation signal generated by the transformer-coupledoscillator. An oscillation frequency of the oscillation signal can betuned by tuning values of the primary capacitor Cp and the secondarycapacitor Cs. Therefore, the primary capacitor Cp and the secondarycapacitor Cs may be tunable capacitors, or capacitance of at least oneof the two capacitors may be tuned by using a control signal.

It should be noted that, in the transformer-coupled oscillator, a drainof one MOS transistor is connected to a gate of the other MOS transistorthrough a transformer. Therefore, in another implementation, the twogates of the transformer-coupled oscillator may be used as the outputend of the transformer-coupled oscillator. Correspondingly, in thedual-mode oscillator obtained by coupling the two transformer-coupledoscillators with the mode switching circuit, two gates of any of thetransformer-coupled oscillators may be used as an output end of thedual-mode oscillator.

As shown in FIG. 2, the mode switching circuit 230 is located betweenthe two transformer-coupled oscillators 210 and 220, and separatelyconnected to drain output ends of the two transformer-coupledoscillators, to couple the two transformer-coupled oscillators 210 and220 into the dual-mode oscillator. The output end of the dual-modeoscillator may be an output end of the transformer-coupled oscillator210, or may be an output end of the transformer-coupled oscillator 220.

The mode switching circuit 230 specifically includes: a control circuitand two mode capacitors C_(mode) coupled to the control circuit. Thecontrol circuit includes a pair of odd mode switches S_(odd1) andS_(odd2) and a pair of even mode switches S_(even1) and S_(even2). Thetwo even mode switches S_(even1) and S_(even2) are each connected inparallel to one mode capacitor C_(mode).

Two ends of the first even mode switch S_(even1) are respectivelyconnected to the drain of the first MOS transistor 211 in thetransformer-coupled oscillator 210 and a drain of a first MOS transistorin the transformer-coupled oscillator 220. Two ends of the second evenmode switch S_(even2) are respectively connected to the drain of thesecond MOS transistor 212 in the transformer-coupled oscillator 210 anda drain of a second MOS transistor in the transformer-coupled oscillator220.

Two ends of the first odd mode switch S_(odd1) are respectivelyconnected to the drain of the second MOS transistor 212 in thetransformer-coupled oscillator 210 and the drain of the first MOStransistor in the transformer-coupled oscillator 220. Two ends of thesecond odd mode switch S_(odd2) are respectively connected to the drainof the first MOS transistor 211 in the transformer-coupled oscillator210 and the drain of the second MOS transistor in thetransformer-coupled oscillator 220.

The two odd mode switches S_(odd1) and S_(odd2) and the two even modeswitches S_(even1) and S_(even2) both may be implemented by using MOStransistors operating in an on/off state, and the switches arecontrolled by using a mode control signal to be turned on and turnedoff.

In this embodiment of this application, the two pairs of switches in themode switching circuit 230 are alternately turned on, to switch anoperating mode of the dual-mode oscillator between an odd mode and aneven mode, and further to change an oscillation frequency range of anoscillation signal that is output by the dual-mode oscillator. Aspecific operating situation is as follows.

(1) When S_(even1) and S_(even2) are turned on and S_(odd1) and S_(odd2)are turned off, the circuit operates in the even mode, and a circuit ofthe dual-mode oscillator is shown in FIG. 3A. In this case, the drainoutput ends of the two transformer-coupled oscillators are directlyconnected by the mode capacitors C_(mode) and the two even mode switchesthat are turned on, and the two oscillators operate in an in-phasestate, that is, two ends of the mode capacitor C_(mode) have a samewaveform, no current passes through the mode capacitor C_(mode), andC_(mode) may be removed equivalently, that is, C_(mode) is equivalent tobeing bypassed. An equivalent circuit is shown in FIG. 3B. Theoscillation frequency range of the dual-mode oscillator is the same asan oscillation frequency range of a single transformer-coupledoscillator.

(2) When S_(odd1) and S_(odd2) are turned on and S_(evens) and S_(even2)are turned off, the circuit operates in the odd mode, and a circuit ofthe dual-mode oscillator is shown in FIG. 4A. In this case, the drainoutput ends of the two transformer-coupled oscillators arecross-connected by the two odd mode switches that are turned on, and arealso connected to the mode capacitors C_(mode), and the twotransformer-coupled oscillators operate in a reverse-phase state, thatis, waveforms at the two ends of the mode capacitor C_(mode) aredifferential output voltages of the two transformer-coupled oscillators.In this case, the mode capacitor C_(mode) may be equivalent to bridgingtwo drain ends of the transformer-coupled oscillators, and an equivalentcircuit is shown in FIG. 4B. In this case, drain capacitance of theentire dual-mode oscillator increases, and the oscillation frequencyrange is lower than the oscillation frequency range of the singletransformer-coupled oscillator.

It can be learned that, compared with a conventional single oscillator,in the dual-mode oscillator provided in this embodiment of thisapplication, switching between the two operating modes is implemented byusing the mode switching circuit, so that oscillation signals having twodifferent bands can be obtained, and the oscillation frequency range iswidened. Moreover, the mode switching circuit couples the twotransformer-coupled oscillators, so that phase noise performance can befurther improved. An oscillation frequency range of a high-frequencyoscillation signal obtained in the even mode is the same as theoscillation frequency range of the single transformer-coupledoscillator, so that the oscillation frequency range of the singletransformer-coupled oscillator can be tuned by tuning values of theprimary capacitor Cp and the secondary capacitor Cs, to tune theoscillation frequency range of the high-frequency oscillation signal ofthe dual-mode oscillator. Moreover, an oscillation frequency range of alow-frequency oscillation signal obtained in the odd mode is related tothe mode capacitors C_(mode), so that the oscillation frequency range ofthe low-frequency oscillation signal of the dual-mode oscillator can betuned by tuning a value of C_(mode). Therefore, in the dual-modeoscillator provided in this embodiment of this application, values ofthe primary capacitor Cp and the secondary capacitor Cs in eachtransformer-coupled oscillator and the mode capacitors C_(mode) in themode switching circuit may be tuned to output oscillation signals havinga wide band.

A main cause for poor phase noise performance of an existing LCoscillator-based dual-mode oscillator is that a drain voltage of one MOStransistor of each LC oscillator is directly injected to a gate of theother MOS transistor (as shown in FIG. 1), leading to a relatively smallgate voltage. In this embodiment of this application, the dual-modeoscillator includes the two transformer-coupled oscillators, the drainof the first MOS transistor in each transformer-coupled oscillator isconnected to the gate of the second MOS transistor through the step-uptransformer, that is, the step-up transformer multiplies a drain voltageswing of the first MOS transistor and then injects a voltage signal tothe gate of the second MOS transistor, so that a larger gate voltageswing is obtained without increasing a supply voltage of the oscillator,and the phase noise performance of the dual-mode oscillator is improved.

In a feasible embodiment of the present disclosure, the differential MOStransistor pair in the transformer-coupled oscillator may bespecifically an NMOS transistor pair. As shown in FIG. 2, the first MOStransistor 211 and the second MOS transistor 212 are both NMOStransistors. In this case, after being connected, the source of thefirst NMOS transistor and the source of the second NMOS transistor maybe grounded through a tail current source (as shown in FIG. 2).Alternatively, the tail current source in FIG. 2 may be removed, and thesource of the first NMOS transistor and the source of the second NMOStransistor are directly grounded. In addition, when the differential MOStransistor pair is an NMOS transistor pair, a center tap of the primaryinductor Lp of the step-up transformer 213 is connected to the powersupply voltage V_(DD), and a center tap of the secondary inductor Ls ofthe step-up transformer is connected to the gate bias voltage V_(gate)of an NMOS transistor (the first NMOS transistor or the second NMOStransistor).

In a feasible embodiment of the present disclosure, the differential MOStransistor pair in the transformer-coupled oscillator may alternativelybe a PMOS transistor pair. For example, in a transformer-coupledoscillator 510 shown in FIG. 5, a source of a first PMOS transistor 511and a source of a second PMOS transistor 512 are both connected to apower supply voltage V_(DD) through a current source (or directlyconnected to the power supply voltage V_(DD)). In addition, a center tapof a primary inductor Lp of a step-up transformer 513 of thetransformer-coupled oscillator 510 is grounded, and a center tap of asecondary inductor Ls is connected to a gate bias voltage V_(gate) of aPMOS transistor (the first PMOS transistor or the second PMOStransistor). Connection manners of the other wiring ends of thetransformer-coupled oscillator 510 are the same as those of thetransformer-coupled oscillator 210, and details are not described hereinagain.

In this embodiment of this application, the two transformer-coupledoscillators in the dual-mode oscillator shown in FIG. 2 may be bothreplaced with the transformer-coupled oscillator 510 shown in FIG. 5, toobtain a dual-mode oscillator in another structure. An operationprinciple of the dual-mode oscillator is the same as the principledescribed above.

In a feasible embodiment of the present disclosure, each of the primarycapacitor Cp and the secondary capacitor Cs in the transformer-coupledoscillator may be implemented by using at least one of a switchcapacitor array or a variable capacitance diode, to obtain a tunablecapacitor, that is, the primary capacitor Cp includes at least one of afirst switch capacitor array or a first variable capacitance diode, andthe secondary capacitor Cs includes at least one of a second switchcapacitor array or a second variable capacitance diode. In thisembodiment, if the primary capacitor Cp and the secondary capacitor Cseach include the switch capacitor array and the variable capacitancediode, stepped tuning on capacitance of the primary capacitor Cp and thesecondary capacitor Cs can be implemented by changing quantities ofenabled capacitors in the switch capacitor arrays, to further implementstepped tuning on an oscillation frequency of the transformer-coupledoscillator; and continuous fine tuning on the capacitance of the primarycapacitor Cp and the secondary capacitor Cs can be implemented by tuningcontrol voltages of the variable capacitance diodes, to furtherimplement continuous fine tuning on the oscillation frequency of thetransformer-coupled oscillator.

Based on the dual-mode oscillator in the foregoing embodiment, anembodiment of this application further provides a multi-phaseoscillator. The multi-phase oscillator includes N dual-mode oscillatorsprovided in any embodiment above and N multi-phase coupled circuits. Nis an integer greater than 1. Any multi-phase coupled circuit is coupledbetween two dual-mode oscillators, and is configured to couple acoupling point of one of the dual-mode oscillators to a coupling pointof the other dual-mode oscillator. A coupling point of any dual-modeoscillator may be an output of the dual-mode oscillator, that is, twodrains of any transformer-coupled oscillator in the dual-modeoscillator, or two gates of any transformer-coupled oscillator in thedual-mode oscillator. A Mobius loop connection is formed by the Ndual-mode oscillators and the N multi-phase coupled circuits. Multiplestages are formed, and each stage includes one dual-mode oscillator andone multi-phase coupled circuit. That is, a first coupling end of amulti-phase coupled circuit at each stage is connected to a dual-modeoscillator at the stage. Second coupling ends of multi-phase coupledcircuits at N−1 of the N stages are each directly connected (in-phaseconnection) to a dual-mode oscillator at a next stage, that is, directlycoupled, and a second coupling end of a multi-phase coupled circuit atthe other stage is crossed and then connected (reverse-phase connection)to a dual-mode oscillator at a next stage, that is, cross-coupled. Inthe multi-phase oscillator provided in this embodiment of thisapplication, a value of N may be an integer such as 2 or 3 or 4. Thefollowing describes a circuit structure of the multi-phase oscillatorwith reference to accompanying drawings by using an example in whichN=4.

In a diagram of a module of a multi-phase oscillator shown in FIG. 6, aMobius loop connection is formed by four dual-mode oscillatorsrespectively numbered 1100, 1200, 1300, and 1400 and four multi-phasecoupled circuits 610, 620, 630, and 640, a four-stage dual-modeoscillator system is formed, and each stage includes one dual-modeoscillator and one multi-phase coupled circuit. A dual-mode oscillatorat each stage includes two transformer-coupled oscillators and a modeswitching circuit connecting the two transformer-coupled oscillators.Mode switching circuits in the dual-mode oscillators at the stages arerespectively numbered 1130, 1230, 1330, and 1430, and performsynchronous switching control by using a same mode control signal.

In this embodiment, a first coupling end of a multi-phase coupledcircuit at each stage is connected to a coupling point of a dual-modeoscillator at the stage, and a second coupling end of the multi-phasecoupled circuit at each stage is connected to a coupling point of adual-mode oscillator at a next stage. Specifically, as shown in FIG. 6,a first coupling end of the multi-phase coupled circuit 610 at the firststage is connected to a coupling point of the dual-mode oscillator 1100at the first stage, and a second coupling end of the multi-phase coupledcircuit 610 at the first stage is connected to a coupling point of thedual-mode oscillator 1200 at the second stage. A first coupling end ofthe multi-phase coupled circuit 620 at the second stage is connected toa coupling point of the dual-mode oscillator 1200 at the second stage,and a second coupling end of the multi-phase coupled circuit 620 at thesecond stage is connected to a coupling point of the dual-modeoscillator 1300 at the third stage. A first coupling end of themulti-phase coupled circuit 630 at the third stage is connected to acoupling point of the dual-mode oscillator 1300 at the third stage, anda second coupling end of the multi-phase coupled circuit 630 at thethird stage is connected to a coupling point of the dual-mode oscillator1400 at the fourth stage. A first coupling end of the multi-phasecoupled circuit 640 at the fourth stage is connected to a coupling pointof the dual-mode oscillator 1400 at the fourth stage, and a secondcoupling end of the multi-phase coupled circuit 640 at the fourth stageis crossed and then connected to a coupling point of the dual-modeoscillator 1100 at the first stage.

The coupling point of the dual-mode oscillator may be two gates or twodrains of any transformer-coupled oscillator in the dual-modeoscillator. That is, in a case with the four stages shown in FIG. 6,there may be 2⁴ connection manners when different transformer-coupledoscillators are selected, including connections between fourtransformer-coupled oscillators respectively numbered 1110, 1210, 1310,and 1410 shown in FIG. 6 and the multi-phase coupled circuits, and alsoincluding connections between four transformer-coupled oscillatorsrespectively numbered 1120, 1220, 1320, and 1410 and the multi-phasecoupled circuits, and the like.

In the diagram of the module shown in FIG. 6, two output ends of each ofthe multi-phase coupled circuit 610 at the first stage, the multi-phasecoupled circuit 620 at the second stage, and the multi-phase coupledcircuit 630 at the third stage are directly connected to a correspondingdual-mode oscillator at a next stage, and only two output ends of themulti-phase coupled circuit 640 at the fourth stage are crossed and thenconnected to a dual-mode oscillator at a next stage, that is, connectedto the transformer-coupled oscillator 1110, to form the Mobius loopconnection. It should be noted herein that, in another embodiment, theMobius loop connection may alternatively be formed by setting two outputends of the multi-phase coupled circuit 610 at the first stage (or themulti-phase coupled circuit 620 at the second stage or the multi-phasecoupled circuit 630 at the third stage) to be cross-connected, andsetting output ends of the other three multi-phase coupled circuits tobe directly connected.

Compared with the existing dual-mode oscillator shown in FIG. 1 that cangenerate differential signals in only two phases, in the multi-phaseoscillator provided in this embodiment of this application, a Mobiusloop is formed by multiple dual-mode transformer-coupled oscillators andmulti-phase coupled circuits, so that oscillation signals in multiplephases can be generated (N pairs of transformer-coupled oscillators cangenerate oscillation signals in 2N phases), and phase noise performanceof the entire oscillator can be improved.

Moreover, in the multi-phase oscillator provided in this embodiment ofthis application, based on a same mode control signal, phases oftransformer-coupled oscillator pairs in the dual-mode oscillators aresynchronously locked to an in-phase or reverse-phase state by using modeswitching circuits, so that only one transformer-coupled oscillator ineach transformer-coupled oscillator pair needs to be connected to amulti-phase coupled circuit, to determine phase output of an entireoscillator array. It can be learned that, the multi-phase oscillatorprovided in this embodiment of this application has a simple circuitstructure, and a corresponding circuit layout is more easilyimplemented.

In a feasible embodiment of this application, the multi-phase coupledcircuits in the multi-phase oscillator may be specifically implementedby using coupling MOS transistor pairs. Correspondingly, the modulediagram shown in FIG. 6 may be specifically a circuit structure shown inFIG. 7A and FIG. 7B.

In this embodiment, the first coupling end of the multi-phase coupledcircuit at each stage is connected to the coupling point of thedual-mode oscillator at the stage, and the second coupling end of themulti-phase coupled circuit at each stage is connected to the couplingpoint of the dual-mode oscillator at the next stage. Specifically, asshown in FIG. 6, the first coupling end of the multi-phase coupledcircuit 610 at the first stage is connected to two drains of thetransformer-coupled oscillator 1110 in the dual-mode oscillator 1100 atthe first stage, and the second coupling end of the multi-phase coupledcircuit 610 at the first stage is connected to two drains of thetransformer-coupled oscillator 1210 in the dual-mode oscillator 1200 atthe second stage. The first coupling end of the multi-phase coupledcircuit 620 at the second stage is connected to two drains of thetransformer-coupled oscillator 1210 in the dual-mode oscillator 1200 ofat the second stage, and the second coupling end of the multi-phasecoupled circuit 620 at the second stage is connected to two drains ofthe transformer-coupled oscillator 1310 in the dual-mode oscillator 1300at the third stage. The first coupling end of the multi-phase coupledcircuit 630 at the third stage is connected to two drains of thetransformer-coupled oscillator 1310 in the dual-mode oscillator 1300 atthe third stage, and the second coupling end of the multi-phase coupledcircuit 630 at the third stage is connected to two drains of thetransformer-coupled oscillator 1410 in the dual-mode oscillator 1400 atthe fourth stage. The first coupling end of the multi-phase coupledcircuit 640 at the fourth stage is connected to two drains of thetransformer-coupled oscillator 1410 in the dual-mode oscillator 1400 atthe fourth stage, and the second coupling end of the multi-phase coupledcircuit 640 at the fourth stage is crossed and then connected to twodrains of the transformer-coupled oscillator 1110 in the dual-modeoscillator 1100 at the first stage.

Referring to FIG. 7A and FIG. 7B, the multi-phase coupled circuit ateach stage includes a coupling MOS transistor pair, two drains of thecoupling MOS transistor pair are used as the first coupling end of themulti-phase coupled circuit, and two gates of the coupling MOStransistor pair are used as the second coupling end of the multi-phasecoupled circuit. Using the multi-phase coupled circuit 640 at the fourthstage as an example, the multi-phase coupled circuit 640 includes afirst coupling MOS transistor 641 and a second coupling MOS transistor642. A source of the first coupling MOS transistor 641 and a source ofthe second coupling MOS transistor 642 are both grounded (directly orthrough a current source). A drain of the first coupling MOS transistor641 is connected to a drain of a first MOS transistor 1411 in thetransformer-coupled oscillator 1410 (a corresponding voltage sign isV₃₊), and a drain of the second coupling MOS transistor 642 is connectedto a drain of a second MOS transistor 1412 in the transformer-coupledoscillator 1410 (a corresponding voltage sign is V³⁻). A gate of thefirst coupling MOS transistor 641 and a gate of the second coupling MOStransistor 642 are respectively connected to drains of two MOStransistors in the transformer-coupled oscillator 1110. Because thesecond coupling end of the multi-phase coupled circuit 640 at the fourthstage is set to be cross-connected, the gate of the first coupling MOStransistor 641 is connected to a drain of a second MOS transistor 1112in the transformer-coupled oscillator 1110 (a corresponding voltage signis V₄₊), and the gate of the second coupling MOS transistor 642 isconnected to a drain of a first MOS transistor 1111 in thetransformer-coupled oscillator 1110 (a corresponding voltage sign isV⁴⁻).

In another embodiment, the second coupling end of the multi-phasecoupled circuit 640 at the fourth stage may alternatively be set to bedirectly connected, and a second coupling end of a multi-phase coupledcircuit at another stage is set to be cross-connected. In this case, inthe multi-phase coupled circuit 640 at the fourth stage, the gate of thefirst coupling MOS transistor 641 is connected to the drain of the firstMOS transistor 1111 in the transformer-coupled oscillator 1110, and thegate of the second coupling MOS transistor 642 is connected to the drainof the second MOS transistor 1112 in the transformer-coupled oscillator1110.

It should be noted herein that, to ensure that a line in an accompanyingdrawing is concise and comprehensible, a connection line between anoutput end of the multi-phase coupled circuit and the dual-modeoscillator at the next stage is not actually drawn in the diagram of thecircuit shown in FIG. 7A and FIG. 7B, and may be determined by a relatedperson according to voltage signs marked in the figure, that is, twoendpoints with a same voltage sign are endpoints actually connected. Inaddition, each transformer-coupled oscillator in FIG. 7A and FIG. 7B isan NMOS transistor-based transformer-coupled oscillator, and in anotherembodiment, may be replaced with the foregoing PMOS transistor-basedtransformer-coupled oscillator in FIG. 5.

In a feasible embodiment of this application, the multi-phase coupledcircuits in the multi-phase oscillator may be specifically implementedby using coupling capacitor pairs. Correspondingly, the module diagramshown in FIG. 6 may be specifically a circuit structure shown in FIGS.8A-8D.

Referring to FIGS. 8A-8D, still using the multi-phase coupled circuit640 at the fourth stage as an example, the multi-phase coupled circuit640 includes a first coupling capacitor C1 and a second couplingcapacitor C2. One end (one first coupling end of the multi-phase coupledcircuit 640 at the fourth stage) of the first coupling capacitor C1 isconnected to a drain of a first MOS transistor 1411 in the dual-modeoscillator at the fourth stage (a corresponding voltage sign is V₃₊),and the other end (one second coupling end of the multi-phase coupledcircuit 640 at the fourth stage) of first coupling capacitor C1 isconnected to a drain of a second MOS transistor 1112 in the dual-modeoscillator at the first stage (a corresponding voltage sign is V₄₊). Oneend (the other first coupling end of the multi-phase coupled circuit 640at the fourth stage) of the second coupling capacitor C2 is connected toa drain of a second MOS transistor 1412 in the dual-mode oscillator atthe fourth stage (a corresponding voltage sign is V³⁻), and the otherend (the other second coupling end of the multi-phase coupled circuit640 at the fourth stage) of second coupling capacitor C2 is connected toa drain of a first MOS transistor 1111 in the dual-mode oscillator atfirst stage (a corresponding voltage sign is V⁴⁻). Wiring manners of theother three multi-phase coupled circuits may be determined withreference to voltage signs in FIGS. 8A-8D, and details are not describedherein.

In another embodiment of this application, the multi-phase coupledcircuits in the multi-phase oscillator may alternatively be implementedby using coupling inductor pairs or coupling microstrips. For acorresponding circuit diagram, refer to FIGS. 8A-8D (that is, thecoupling capacitor pair in FIG. 8 is replaced with the coupling inductorpair or the coupling microstrips).

In the multi-phase oscillator in the foregoing embodiment, two firstcoupling ends and two second coupling ends of a multi-phase coupledcircuit are all connected to drains of MOS transistors in acorresponding dual-mode oscillator. In another feasible embodiment ofthis application, the two first coupling ends and the two secondcoupling ends of the multi-phase coupled circuit may alternatively beconnected to gates of MOS transistors in the corresponding dual-modeoscillator, as shown in FIGS. 9A-9D. In a circuit shown in FIGS. 9A-9D,N is still 4, and wiring manners of multi-phase coupled circuits aredetermined according to voltage signs in FIGS. 9A-9D, so that thecircuit diagram is concise and comprehensible.

Based on the circuit shown in FIG. 7A and FIG. 7B, in this embodiment ofthe present disclosure, a dual-mode eight-phase oscillator is designedby using a Complementary Metal Oxide Semiconductor (CMOS) procedure.Eight-phase output is implemented by means of circuit post-sim display,and waveforms are shown in FIG. 10 (a horizontal coordinate is time, inunit of nanosecond (ns), and a vertical coordinate is voltage V, in unitof volt (V)), and a frequency range is: 29.97 to 37.91 gigahertz (GHz)in an even mode, and 26.03 to 30.51 GHz in an odd mode.

The following Table 1 describes performance comparison between themulti-phase oscillator provided in this embodiment of this applicationand oscillators (an oscillator ISSCC2013 based on the CMOS procedure, anoscillator ISSCC2013 based on a Silicon Germanium (SiGe) procedure, andan oscillator ISSCC2016 based on the CMOS procedure) disclosed in recentyears. Figure of Merit (FoM) means comprehensively considering qualityfactors of an oscillator such as a frequency, power consumption, andphase noise of the oscillator, and Figure of Merit With Tuning Range(FoM_(T)) means comprehensively considering quality factors of anoscillator: a frequency, power consumption, phase noise, and a frequencyrange of the oscillator. Their expressions are respectively as follows:

FoM=20 log(f ₀ /Δf)−PN−10 log(P _(Dc)/1 mW); and

FoM _(T)=20 log(f ₀ /Δf·FTR/10)−PN−10 log(P _(DC)/1 mW).

In the foregoing formulas, f₀ represents an oscillation frequency, Δfrepresents a frequency deviation corresponding to phase noise, FrequencyTuning Range (FTR) represents a frequency tuning range, Phase Noise (PN)represents a phase noise value, P_(DC) represents direct current powerconsumption, and 1 mW is a unit power value of 1 milliwatt.

TABLE 1 Performance comparison between the oscillators Present ISSCC2013ISSCC2013 ISSCC2016 Disclosure Procedure CMOS SiGe CMOS CMOS Supplyvoltage 1 1.5 1.3 1 (V) Frequency range 33.6-46.2 28-37.8 26.5-29.726-37.9 (GHz) Frequency range 31.6 29.8 11.4 37.2 (%) Power 9.8 10.538.6 11.5 consumption (mW) Phase noise −97 −103.6 −106.8 −103.5 @1M(dBc/Hz) FoM (dBc/Hz) 180 183.9 179.4 182.9 FoM_(T) (dBc/Hz) 189.9 193.5180.54 194.3 Phase 2 2 4 8

It can be learned from a comparison result in Table 1 that, better FoMand FoM_(T) are obtained by using the CMOS procedure in comparison withanother CMOS design. It can be learned that, the oscillator provided inthis embodiment of this application can comprehensively satisfyrequirements for low power consumption, high phase noise performance, awide frequency range, and multiple phases, and is advantageous inmanufacturing costs.

The foregoing descriptions are implementations of this application, butare not intended to limit the protection scope of this application. Thestructure in the foregoing embodiment may be applied to the field ofintegrated circuits. The term “connect” used in the embodiments of thepresent disclosure indicates a coupling relationship in signal. Forexample, a signal may be transmitted by connecting one endpoint toanother endpoint, and such a connection may include a direct or indirectconnection.

1. A dual-mode oscillator, comprising: two transformer-coupledoscillators; and a mode switching circuit electrically coupled to eachtransformed-coupled oscillator, wherein the each transformer-coupledoscillator comprises a differential metal oxide semiconductor (MOS)transistor pair, a primary capacitor, a secondary capacitor, and astep-up transformer, wherein a first source of a first MOS transistor inthe differential MOS transistor pair and a second source of a second MOStransistor in the differential MOS transistor pair are both electricallycoupled to a constant-voltage node, wherein a first drain of the firstMOS transistor in the differential MOS transistor pair is connected toone end of the primary capacitor and to a first input end of the step-uptransformer, wherein a second drain of the second MOS transistor in thedifferential MOS transistor pair is connected to an other end of theprimary capacitor and to a second input end of the step-up transformer,wherein a first gate of the first MOS transistor in the differential MOStransistor pair is connected to one end of the secondary capacitor andto a second output end of the step-up transformer, wherein a second gateof the second MOS transistor in the differential MOS transistor pair isconnected to an other end of the secondary capacitor and to a firstoutput end of the step-up transformer, wherein the first input end andthe first output end are dotted terminals, wherein the mode switchingcircuit is located between the two transformer-coupled oscillators andis separately connected to two drains of the each transformer-coupledoscillator, and wherein the mode switching circuit is configured tochange an oscillation frequency range output by the dual-mode oscillatorusing switching.
 2. The dual-mode oscillator according to claim 1,wherein the first MOS transistor and the second MOS transistor are bothN-channel MOS (NMOS) transistors, wherein the first source of the firstMOS transistor and the second source of the second MOS transistor areconnected to the constant-voltage node, and wherein the constant-voltagenode is either directly grounded or is grounded through a tail currentsource.
 3. The dual-mode oscillator according to claim 2, wherein thestep-up transformer comprises a primary inductor and a secondaryinductor Ls, wherein a center tap of the primary inductor is connectedto a power supply voltage, and wherein a center tap of the secondaryinductor is connected to a gate bias voltage.
 4. The dual-modeoscillator according to claim 1, wherein the first MOS transistor andthe second MOS transistor are both P-channel MOS (PMOS) transistors,wherein the first source of the first MOS transistor and the secondsource of the second MOS transistor are connected to theconstant-voltage node, and wherein the constant-voltage node is eitherdirectly connected to a power supply voltage or is connected to thepower supply voltage through a tail current source.
 5. The dual-modeoscillator according to claim 4, wherein a center tap of a primaryinductor of the step-up transformer is grounded, and wherein a centertap of a secondary inductor of the step-up transformer is connected to abias voltage.
 6. The dual-mode oscillator according to claim 1, whereinat least one of the primary capacitor and the secondary capacitorcomprises a switch capacitor array, a tunable variable capacitancediode, or a combination of the switch capacitor array and the tunablevariable capacitance diode.
 7. The dual-mode oscillator according toclaim 1, wherein the mode switching circuit comprises: a controlcircuit; and at least two mode capacitors coupled to the controlcircuit, wherein the control circuit is configured to switch thedual-mode oscillator between an odd mode and an even mode under aneffect of a mode control signal, wherein the at least two modecapacitors are equivalent to being bypassed and the oscillationfrequency range is a first oscillation frequency range in the odd mode,wherein the at least two mode capacitors are equivalent to bridging thetwo drains of the each transformer-coupled oscillators and theoscillation frequency range is a second oscillation frequency range inthe even mode, and wherein the second oscillation frequency range isdifferent from the first oscillation frequency range.
 8. The dual-modeoscillator according to claim 7, wherein the control circuit comprises:a first odd mode switch and a second odd mode switch; and a first evenmode switch and a second even mode switch, wherein each of the firsteven mode switch and the second even mode switch is connected inparallel to at least one capacitor of the at least two mode capacitors,wherein each end of the first even mode switch is separately connectedto drains of first MOS transistor of the two transformer-coupledoscillators, wherein each end of the second even mode switch isseparately connected to drains of second MOS transistors of the twotransformer-coupled oscillators, wherein each end of the first odd modeswitch is respectively connected to a drain of the first MOS transistorof one transformer-coupled oscillator and a drain of the second MOStransistor of an other transformer-coupled oscillator, wherein each endof the second odd mode switch is respectively connected to a drain ofthe second MOS transistor of the one transformer-coupled oscillator anda drain of the first MOS transistor of other transformer-coupledoscillator, wherein the first odd mode switch and the second odd modeswitch are turned on and the first even mode switch and the second evenmode switch are turned off in the odd mode, and wherein the first oddmode switch and the second odd mode switch are turned off and the firsteven mode switch and the second even mode switch are turned on in theeven mode.
 9. The dual-mode oscillator according to claim 7, wherein thesecond oscillation frequency range is lower than the first oscillationfrequency range.
 10. A multi-phase oscillator, comprising: N dual-modeoscillators; and N multi-phase coupled circuits, wherein N is an integergreater than 1, wherein each multi-phase coupled circuit is coupledbetween two dual-mode oscillators, wherein a Mobius loop connection isformed by the N dual-mode oscillators and the N multi-phase coupledcircuits, wherein each dual-mode oscillator comprises twotransformer-coupled oscillators and a mode switching circuit, whereineach transformer-coupled oscillator comprises a differential metal oxidesemiconductor (MOS) transistor pair, a primary capacitor, a secondarycapacitor, and a step-up transformer, wherein a first source of a firstMOS transistor in the differential MOS transistor pair and a secondsource of a second MOS transistor in the differential MOS transistorpair are coupled to a constant-voltage node, wherein a first drain ofthe first MOS transistor in the differential MOS transistor pair isseparately connected to one end of the primary capacitor and to a firstinput end of the step-up transformer, wherein a second drain of thesecond MOS transistor in the differential MOS transistor pair isconnected to an other end of the primary capacitor and to a second inputend of the step-up transformer, wherein a first gate of the first MOStransistor in the differential MOS transistor pair is separatelyconnected to one end of the secondary capacitor and to a second outputend of the step-up transformer, wherein a second gate of the second MOStransistor in the differential MOS transistor pair is separatelyconnected to an other end of the secondary capacitor and to a firstoutput end of the step-up transformer, wherein the first input end andthe first output end are dotted terminals, wherein the mode switchingcircuit is located between the two transformer-coupled oscillators andis separately connected to two drains of the each transformer-coupledoscillator, and wherein the mode switching circuit is configured tochange an oscillation frequency range output by the dual-mode oscillatorusing switching.
 11. The multi-phase oscillator according to claim 10,wherein the N dual-mode oscillators form N-stages with the N multi-phasecoupled circuits, wherein each stage comprises one dual-mode oscillatorand one multi-phase coupled circuit, wherein a first coupling end of amulti-phase coupled circuit at the each stage is connected to two drainsof any transformer-coupled oscillator in a dual-mode oscillator at astage, and wherein a second coupling end of the multi-phase coupledcircuit at the each stage is connected to the two drains of the anytransformer-coupled oscillator in the dual-mode oscillator at a nextstage.
 12. The multi-phase oscillator according to claim 10, wherein theN dual-mode oscillators form N-stages with the N multi-phase coupledcircuits, wherein each stage comprises one dual-mode oscillator and onemulti-phase coupled circuit, wherein the first coupling end of themulti-phase coupled circuit at the each stage is connected to two gatesof any transformer-coupled oscillator in a dual-mode oscillator at astage, and wherein a second coupling end of the multi-phase coupledcircuit at the each stage is connected to the two gates of the anytransformer-coupled oscillator in the dual-mode oscillator at a nextstage.
 13. The multi-phase oscillator according to claim 12, wherein themulti-phase coupled circuit comprises a coupling MOS transistor pair,wherein a first source of the first MOS transistor in the coupling MOStransistor pair and the second source of the second MOS transistor inthe coupling MOS transistor pair are connected and either directlygrounded or grounded through a current source, wherein a first drain ofthe first MOS transistor and a second drain of the second MOS transistorare used as the first coupling end and are connected to the two drainsor the two gates of the any transformer-coupled oscillator in thedual-mode oscillator at the first stage, and wherein the first gate ofthe first MOS transistor and the second gate of the second MOStransistor are used as the second coupling end and are connected toeither the two drains or the two gates of the any transformer-coupledoscillator in the dual-mode oscillator at the next stage.
 14. Themulti-phase oscillator according to claim 11, wherein each N multi-phasecoupled circuit comprises a coupling MOS transistor pair, a couplingcapacitor pair, a coupling inductor pair, and a coupling microstrip. 15.The multi-phase oscillator according to claim 10, wherein the first MOStransistor and the second MOS transistor are both N-channel MOS (NMOS)transistors, wherein each of the first source of the first MOStransistor and the second source of the second MOS transistor areconnected to the constant-voltage node, and wherein the constant-voltagenode is either directly grounded or is grounded through a tail currentsource.
 16. The multi-phase oscillator according to claim 15, wherein acenter tap of a primary inductor of the step-up transformer is connectedto a power supply voltage, and wherein a center tap of a secondaryinductor of the step-up transformer is connected to a bias voltage. 17.The multi-phase oscillator according to claim 10, wherein the first MOStransistor and the second MOS transistor are both P-channel MOS (PMOS)transistors, wherein the first source of the first MOS transistor andthe second source of the second MOS transistor are coupled to theconstant-voltage node, and wherein the constant-voltage node is eitherdirectly connected to a power supply voltage or is connected to thepower supply voltage through a tail current source.
 18. The multi-phaseoscillator according to claim 17, wherein a center tap of a primaryinductor of the step-up transformer is grounded, and wherein a centertap of a secondary inductor of the step-up transformer is connected to abias voltage.
 19. The multi-phase oscillator according to claim 10,wherein at least one of the primary capacitor and the secondarycapacitor comprises a switch capacitor array, a variable capacitancediode tunable by a tuning signal, or a combination of the switchcapacitor array and the variable capacitance diode tunable by the tuningsignal.
 20. The multi-phase oscillator according to claim 10, whereinthe mode switching circuit comprises: a control circuit; and at leasttwo mode capacitors coupled to the control circuit, wherein the controlcircuit is configured to switch the dual-mode oscillator between an oddmode and an even mode under an effect of a mode control signal, whereinthe at least two mode capacitors are equivalent to being bypassed andthe oscillation frequency range is a first oscillation frequency rangein the odd mode, wherein the at least two mode capacitors are equivalentto bridging the two drains of the each transformer-coupled oscillatorand the oscillation frequency range is a second oscillation frequencyrange in the even mode, and wherein the second oscillation frequencyrange is different from the first oscillation frequency range.